Sally Hawkins stars as Poppy, the grinning, goofy first-grade teacher at the heart of Mike Leigh’s latest look at the British working class, Happy-Go-Lucky.

Miramax Films / Simon Mein

Poppy is insufferably, unbearably upbeat. Always with a smile, laughing even when she’s in pain, she wears you down with her sweetness and light. If only she weren’t so maddeningly adorable.

Poppy (Sally Hawkins) is the grinning, goofy heart of British filmmaker Mike Leigh’s latest scripted improv about the English working class. And even if we never learn what’s made her so Happy-Go-Lucky, we can sense an inner sorrow, a loneliness that Hawkins hides behind Poppy’s daffy boots and rubber ducky earrings and dizzy habit of joking about everything.

Her bike’s been stolen? “Oh, no. I never even got to say goodbye!”

Her first-grade students may adore her; her sisters tolerate her. But Poppy is a klutzy test to her flamenco dancing instructor, a high-strung Spaniard (Karina Fernandez, worth the price of admission). And the irresistible goof meets the immovable grump when the bike-less Poppy begins taking driving lessons.

Leigh, a true actor’s director in that the actors help him script his films, turns Hawkins loose on the great Leigh-vet Eddie Marsan (Vera Drake) as Scott, a seething misanthropist who takes his driving instruction deadly serious.

“We’re going to listen and concentrate,” he begins, but Poppy will do neither. “You can’t control a car in high heels,” he tells her, lesson after lesson. She ignores him.

“You celebrate chaos!” he spits. Literally.

“Are you a Satanist, Scott?” she fires back, disarmingly.

In most Leigh films, there isn’t a vast arc to the characters. As in Life Is Sweet or Secrets and Lies, these are just everyday people going through a little stretch of life. But as perfectly observed as Leigh’s life-slices are, the effort shows in this one. Poppy and roommate Zoe (Alexis Zegerman, quite good) engage in a staring contest that feels like an improvisation exercise. The banter, though often clever, can seem too polished.

Then there’s the moment when we watch Poppy and a social worker quietly question a little boy who’s become a bully, gently probing, finding the source of the problem. That’s when you see the value in Leigh’s patience, letting the scene and the actors find their own rhythm and truth.

Hawkins wears her grin in almost every scene, but she gives us hints that this dizzy 30-year-old is deep, as are the disappointments that might have caused Poppy to don this mask. It’s a performance of sustained, childlike wonder and adult wit.

And when she hops into that car with Scott, we genuinely fear for her, hope for her and hope that somehow she can bring this hopelessly angry, hateful man some peace, even though we suspect that hope is in vain.

****Happy-Go-Lucky

Starring: Sally Hawkins, Eddie Marsan, Karina Fernandez.

Rated: R, contains profanity.